A packaging laminate of the type described above is previously known in the art from, for example, International Patent Application PCT/SE2011/050978.
The packaging laminate according to International Patent Application PCT/SE2011/050978 has a rigid, but foldable layer of paper or paperboard and outer, heat-resistant layers of plastic on both sides of the paper or paperboard layer. Between the paper or paperboard layer and one of the outer, heat-resistant plastic layers, the prior art packaging laminate has at least one further layer possessing tightness properties vis-à-vis gases, in particular oxygen gas. One preferred example of such a gas tightness layer is an aluminium foil (Alifoil) which moreover makes for thermosealing of the packaging laminate by so-called induction thermosealing which is a both rapid, simple and efficient sealing technology.
Since a paper or paperboard surface often has a coarse and uneven surface profile which impedes direct printing on the paper or paperboard layer with constant good print quality, it is, in certain cases, necessary to pre-treat, for purposes of improving quality, the paper or paperboard surface which is to be printed and decorated with printing ink. To this end, the paper or paperboard layer in the prior art packaging laminate displays, on that side which is intended to be printed with printing ink, a smooth printable coating of pigment and binder or adhesive in contact with the paper or paperboard layer.
The prior art packaging laminate according to the foregoing is produced from a web of paper or paperboard which, on its one side, has a printable coating of pigment and adhesive. The web is unwound from a magazine reel and led through a printing station in which the web, on its pigment-coated side, is provided with the desired decorative artwork of printing ink which is printed direct on the printable coating. From the printing station, the paper or paperboard web now provided with decorative artwork is led further to a lamination station in which the other, or uncoated, side of the web is provided with a layer of a material possessing desirable tightness properties vis-à-vis gases, e.g. an aluminium foil, which is laminated to the paper or paperboard web. From the lamination station, the laminated web is led to a coating station in which the web is finally coated with outer, heat-resistant layers of plastic which are extruded on both sides of the web, whereafter the web is wound up for further handling and use.
From the prior art packaging material, packages are produced using modern packing and filling machines, which, from a web or from prefabricated blanks of the packaging material, produce filled, sealed packages.
From, for example, flat folded tubular blanks of the packaging material, packages are thus produced in that the packaging blank is first raised to an open packaging carton. The one end of the packaging carton (e.g. the bottom end) is sealed by fold forming and thermosealing of the corresponding foldable bottom panels of the packaging carton. The packaging carton provided with a bottom is filled with optional food, whereafter the other, open end of the packaging carton (in this example the top end) is sealed by an additional fold forming and thermosealing of the corresponding foldable top panels of the packaging carton.
There occur on the market so-called retortable packages or cartons which are intended to be filled with food and, after sealing, subjected to a shelf-life extending heat treatment in a retort with steam as the heat medium. Analogous with so-called aseptic packages (of which the parallelepipedic package entitled Tetra Brik Aseptic is the predominant package on the market), the retortable packages possess the ability to be able to store the packed food for several months and even longer at ambient temperature, without the food deteriorating or being destroyed before its recommended “best before date”. One well-known example of such packages is those marketed under the name Tetra Recart.
Packing containers of the prior art packaging laminate possess many valuable advantages, not least for the consumer. They are mechanically strong and dimensionally stable, at the same time as they are both easy to open and convenient to use. Moreover, they possess the advantage over corresponding preserve cans of sheet metal and plastic that, after emptying, they may readily be compressed to only minimum space requiring planar sheets by simple manual flattening.
However, with the prior art packaging laminate, it not seldom occurs that problems with undesirably uneven print quality arise in connection with printing of the pigment-coated paper or paperboard web. In particular, it has proved that such problems are often caused by fibre dust which has been released from the freely exposed fibre surface of the paper or paperboard web and transferred to and adhered on the surface of the printable coating when the web coated on one side is wound up from the paper machine which produce the web. When the wound up web is subsequently unwound for printing and further processing into finished packaging laminate, released fibre dust thus accompanies the web adhering to the pigment coating of the paper or paperboard web into the printing station where the dust thus counteracts and impedes printing direct on the printable coating.
There is thus a need in the art for an improved packaging laminate which is both easier and simpler to produce without accompanying problems of the type which are associated with printing of the prior art packaging laminate.